The demand for all fossil fuels combined is expected to double by the year 2000. This increased demand is expected even with the increasing use of nuclear power. While the domestic supply of crude oil and of natural gas is not likely to keep pace with the energy demand, alternative energy sources such as coal, oil shale and biomass can play an important role in filling such a gap and thus reduce the requirements for imported supplies of oil and gas.
These alternative fuel sources contain various amounts of nitrogen due to the nature of their origin. When these alternate fuels are combusted, nitrogen oxides are formed. In general, a certain amount of nitrogen oxide is generated thermally during combustion from nitrogen present in the air. However, for the most part, nitrogen oxides generated during combustion are due to fixed nitrogen present in the fuel source. Unfortunately, many of these alternative fuel sources contain relatively high amounts of fixed nitrogen and therefore pose severe environmental problems due to nitrogen oxides emissions during combustion.
Since environmental standards regarding the emission of nitrogen oxides during combustion are expected to become increasingly more stringent, there is a need for an economical method for ensuring that emissions of nitrogen oxides are maintained at acceptable levels during combustion of any fuel and particularly during combustion of high fixed nitrogen alternative fuels.
In general, during combustion of fossil fuels, nitric oxide and nitrogen dioxide are the only two oxides of nitrogen produced in significant quantities. Attempts at removing nitric oxide from gas streams utilizing iron oxides as a catalyst has shown some promise. For example, Moriguchi in his U.S. Pat. No. 4,025,604 discloses the use of iron oxide to catalyze the reduction of nitric oxide by ammonia. However, this process requires the use of large quantities of ammonia and must be carried out at relatively high temperatures. Iron oxide has also been used by Meguerian as disclosed in U.S. Pat. No. 4,104,360, in which iron oxide is used to catalyze the reduction of nitric oxide by carbon monoxide and hydrogen. The necessary presence of carbon monoxide and hydrogen or ammonia is many times undesirable.
Iron pyrite (i.e. FeS.sub.2) has also been used to reduce nitric oxide emissions. For example, Gertsen in U.S. Pat. No. 3,695,828 utilizes iron pyrite and water to remove nitrogen oxides from gas streams. In this process the iron pyrite reacts with the nitric oxide to form, inter alia, nitrogen and sulfuric acid. This process is undesirable because of the production of sulfuric acid which is inherently produced because of the sulfur present in the pyrite.
It is therefore apparent that there is a present need for a method of removing nitric oxide from a gas stream where the nitric oxide removing material is inexpensive, readily available and does not produce unwanted by-products.